B2N2 - When you re calculate for full length, your lovely performance software may well give you a greater flex temp/derate moving your V1 back down the runway making it relevant again. This ,for me, kinda makes your first argument irrelevant. For me, the risks of putting in wrong performance data during that 1min backtrack far outweigh the benefits... There is always a flip side - Our engineers would of course point to the benefits of the increased engine life!
Tomaski - In EU land (if I recall correctly!) we start the 'obstacle accountability area' at the end of the TODA, not at the liftoff point. So for our regs, that wouldn't change this side of the pond...